This invention relates to a process for manufacturing semiconductor devices, and more particularly to a method of mirror-polishing the rear surface of a semiconductor wafer without damaging an electronic component formed on the front surface thereof.
A conventional process for manufacturing semiconductor devices generally comprises the steps of grinding and polishing the rear surface of a semiconductor wafer, on the front surface of which an electronic component is formed. These steps are necessary to grind the wafer down to a predetermined thickness and to thereafter polish the ground surface so that a film of metal, such as Au, can be formed thereon by vapor deposition.
FIG. 3A through FIG. 3C are schematic cross-sectional views showing the steps involved in such conventional grinding and polishing operations. Referring to FIG. 3A a semiconductor wafer 11 of initial thickness Ta has an electronic component 12, such as a transistor, formed on its front surface. The rear surface 13a of the wafer is usually ground down by a rotating grindstone apparatus to a thickness Tb as shown in FIG. 3B, which leaves an unacceptably rough or rippled rear surface 13b. A polishing step is thus performed in order to provide a smooth rear surface 13c as shown in FIG. 3C, with the final wafer thickness being further reduced to the dimension Tc.
Mechanical polishing may be implemented using a rotating disk and a pressure head, as disclosed in U.S. Pat. No. 4,141,180. A chemical polishing method has also been commonly used. These conventional methods have some disadvantages. In the mechanical method, when the rough rear surface 13b of the wafer 11 is polished, the extremely miniaturized and delicate electronic component 12 formed on the front surface of the wafer is susceptible to damage because it is pinched under pressure between the polishing disk and the pressure head. With polishing by the chemical method, on the other hand, a portion of the electronic component 12 is liable to be etched away or damaged by the caustic chemical agent used.